This invention relates to an anti-reflective coating and to a method for fabricating a semiconductor device including the steps of depositing and etching an anti-reflective coating.
The fabrication of semiconductor devices relies repeatedly on the photo lithographic transfer of a pattern from a mask onto the surface of a coated semiconductor wafer. During the photo lithographic process light passes through the patterned mask and the pattern is transferred to a photoresist layer coating the wafer. Ideally the pattern on the mask is exactly replicated in the photoresist layer. When the photoresist layer is coated on a highly reflective film such as a metal layer or a polycrystalline silicon layer, however, light reflections from the reflective layer can interfere with the exact replication of the pattern. Light that is off-normal can be reflected back through the photoresist layer to expose portions of the layer that were intended to be masked. This is especially significant if there are severe steps in the topography of the underlying substrate because incident light can be reflected off those severe steps and again cause unwanted exposure of the photoresist coating.
Organic anti-reflective coating (ARC) films have been extensively used in the semiconductor industry to reduce reflectivity and to ameliorate the above-described problem. The organic ARC films have not been totally satisfactory, however, especially as the devices being fabricated have become more complex, feature sizes of those devices have been reduced, and surface topography has become less planar. The organic ARC films tend to be relatively thick, non-uniform in thickness because applied as a liquid, and generally unable to maintain critical dimensions on the device. This is especially true as the photo lithographic systems have shifted to shorter wavelengths.
Because of the shortcomings of organic ARC films, the semiconductor industry is looking toward inorganic ARC films. The inorganic anti-reflective coatings reduce the undesired reflected light by phase-shift cancellation of specific wavelengths. Conventional inorganic ARC films, however, are not easily integrated into the process for fabricating some of the complex, state of the art semiconductor devices. Problems arise both with the deposition of inorganic ARC films having the desired properties and with the subsequent removal of those films at the completion of the photo lithographic process.
In accordance with the various embodiments of the present invention an anti-reflective coating which overcomes problems attendant with previous photo lithographic processes is described. Also described is a process for forming and subsequently removing an anti-reflective coating and for the fabrication of a semiconductor device.